The invention relates to a pigment composition which comprises azo pigments and auxochromes, a process for the preparation of the composition by coupling an aromatic diazonium compound with 3-hydroxy-2-naphthoic acid, a process for toning an azo lake pigment composition and the use of auxochromes with azo lake pigments.
Azo pigments produced by using 3-hydroxy-2-naphthoic acid as a coupling component are known and particularly useful. For example, they include Pigment Red 57:1 and Pigment Red 48:2. These azo pigments find a diversity of applications and are mainly used to colour printing inks, paints, oil and water colors, plastics and cosmetics. There is a wide range of requirements expected from the pigments used in these applications. For example, a high degree of brilliance and transparency is required for printing inks; durability and hiding power for paints; and heat resistance for plastics. Due to the diversity and extent of these requirements, there is a high demand for pigment compositions which contain known and well-established azo pigments, but permit a wide range of uses according to the intended fields of application.
There is a specific need for improving the toning of azo lake pigment compositions. The term toning, as used in the context of the instant specification, means the control and improvement of properties, such as hue and brilliance.
Brilliance, transparency or hiding power of a pigment composition can be intensified by applying physical methods, such as varying the fineness, form, shape and surface properties of the pigment particles.
The prior art also proposes alternative routes for achieving these goals. It has been recommended to modify the chemical structure of a small amount of pigment in the composition. This can either be achieved by modifying the structure of the 2-hydroxy-3-naphthoic acid. These chemically modified additives present in pigment compositions may be defined as auxochromes. According to EP-A-202 906, the carboxy group in the 2-hydroxy-3-naphthoic acid coupling component is derivatised to an amide or to a substituted amide. According to EP-A-259 007, part of the 2-hydroxy-3-naphthoic acid is replaced with binaphthol.
It is also known to add an auxochrome to azo pigments such as Pigment Red 57:1 in order to obtain shading and depth effects. Auxochromes for Pigment Red 57:1 to obtain blue shading effects have been produced by coupling Tobias acid (2-amino-1-napthalenesulfonic acid) onto 2-hydroxy-3-naphthoic acid. However, the resulting blue shade products still appear xe2x80x9cdirtyxe2x80x9d.
Therefore, the object of this invention was to provide azo lake pigment compositions with an improved quality of shading. Preferably, the masstone, particularly for heatset applications, and transparency of the ink in an oil ink system should be improved.
Accordingly, the claimed pigment composition has been found wherein the auxochrome component of the pigment compositions can be prepared by coupling a 2-hydroxy-3-naphthoic acid component with a phenyl amine component, wherein the phenyl group is substituted by at least one C1-C4-alkoxy substituent, particularly methoxy.
The present invention relates to a pigment composition which comprises at least one pigment of the formula: 
wherein X represents hydrogen or a cation from a metal selected from calcium, barium, strontium, magnesium, manganese and aluminium, R1, R2 and R3 represent hydrogen or members from the group consisting of C1-C4-alkyl, phenyl, halogen, xe2x80x94NO2 and xe2x80x94CF3, and R4 is as defined as R1, R2 and R3 or represents a group of the partial formula 
wherein Xxe2x80x2 is as defined as X above and R1xe2x80x2, R2xe2x80x2 and R3xe2x80x2 are as defined as R1, R2 and R3 under the formula (I) above, and at least one auxochrome of the formula 
wherein Xxe2x80x3 is as defined as X under the formula (I) above, at least one of R5, R6, R7, R8 and R9 represents C1-C4-alkoxy and R5, R6, R7, R8 and R9 independently of one another additionally represent members selected from the group consisting of hydrogen, C1-C4-alkyl, phenyl, halogen, xe2x80x94SO3xe2x80x94H, xe2x80x94NO2 and xe2x80x94CF3 and R7 additionally represents a group of the partial formula 
wherein Xxe2x80x2xe2x80x3 is as defined as X under the formula (I) above, R5, R6, R8 and R9 are as defined as R5, R6, R7 and R8 under the formula (II) above.
A preferred embodiment of the present invention relates to a composition, which comprises at least one pigment of the formula (I), wherein X represents hydrogen or a cation from a metal selected from calcium, barium, strontium, magnesium, manganese and aluminium and R1, R2, R3 and R4 represent hydrogen or members from the group consisting of C1-C4-alkyl, phenyl, halogen, xe2x80x94NO2 and xe2x80x94CF3, and an auxochrome of the formula (II), wherein X is as defined under the formula (I) above, at least one of R5, R6, R7, R8, and R9 represents C1-C4-alkoxy and R5, R6, R7, R8, and R9 independently of one another additionally represent members selected from the group consisting of hydrogen, C1-C4-alkyl, phenyl, halogen, xe2x80x94SO3xe2x80x94H, xe2x80x94NO2 and xe2x80x94CF3.
A particularly preferred embodiment of the present invention relates to composition, which comprises at least one pigment of the formula 
wherein R1 and R2 are different, R1 represents hydrogen, C1-C4-alkyl or halogen and R2 represents C1-C4-alkyl or halogen and X represents hydrogen or a cation from a metal selected from calcium, barium, strontium, magnesium, manganese and aluminium, and an auxochrome (II).
Particularly preferred is a composition, which comprises a pigment (Ixe2x80x2), wherein R1 and R2 are different, R1 represents hydrogen, methyl or chloro and R2 represents methyl or chloro, and an auxochrome (II).
Especially preferred is a composition, which comprises Pigment Red 57:1 and an auxochrome (II) such as an auxochrome obtained by the coupling of ortho-nitro-para-anisidine (ONPA), para-cresidine-orthosulphonic acid (PCOS) or para-nitro-ortho-anisidine (PNOA) with 2-hydroxy-3-naphthoic acid (BONA).
The present invention also relates to compositions comprising preferred auxochromes. In this context a composition is particularly preferred, which comprises at least one pigment (I) and an auxochrome of the formula 
wherein Xxe2x80x3 is as defined as X under the formula (I) above and R7 represents hydrogen or xe2x80x94NO2.
In the pigment composition according to the present invention, the amount of auxo-chrome (II) added to the pigment (I) is from about 0.01 to 10.0%, particularly 0.1 to 5.0%, and especially 0.2 to 2.0% by weight based on the weight of the pigment.
The present invention also relates to a composition, which comprises at least one pigment of the formula (I) of above, an auxochrome of the formula (II) of above and the coupling product of 2-napthylamine-1-sulphonic acid (Tobias acid) with the coupling component (V), particularly 2-hydroxy-3-naphthoic acid.
The pigment composition according to the present invention usually is prepared by methods which are known per se, e.g. by diazotising in situ an aromatic amine and coupling the resulting aromatic diazonium compound with 3-hydroxy-2-naphthoic acid.
The present invention also relates to the process for the preparation of the pigment composition, which comprises diazotising at least one amine of the formula 
wherein R1, R2 and R3 are as defined above and R4 is as defined as R1, R2 and R3 or represents a group of the partial formula 
wherein R1, R2 and R3 are as defined as R1, R2 and R3 above; and at least one amine of the formula 
wherein at least one of R5, R6, R7, R8, and R9 represents C1-C4-alkoxy and R5, R6, R7, R8, and R9 are as defined above and R7 additionally represents a group of the partial formula 
wherein R5xe2x80x2, R6xe2x80x2, R8xe2x80x2 and R9xe2x80x2 are as defined above, and coupling the diazotised amines (III) and (IV) with a coupling component of the formula 
wherein X is as defined above under formula (I).
The process for preparing the pigment composition can be carried out in a customary way and is not particularly restricted. For example the mixture of amines (III) and (IV) preferably is diazotised at xe2x88x9210 to 10xc2x0 C. to prepare the diazo component. The coupling component (V) usually is dissolved in an aqueous solution of sodium hydroxide to prepare the solution of the coupling component. As a rule the diazo component is added dropwise to the aqueous solution containing the coupling component to perform the coupling reaction at a temperature of generally xe2x88x925 to 50xc2x0 C., preferably xe2x88x922 to 20xc2x0 C. The resulting slurry may then be laked with an aqueous salt solution containing metal salts selected from calcium, barium, strontium, magnesium, manganese and aluminium salts or mixtures thereof.
In a preferred embodiment of the process, auxochromes are prepared by diazotising 2- or 4-nitro para anisidine, ortho anisidine-5-sulphonic acid, or para cresidine ortho sulphonic acid and coupling with 3-hydroxy-2-naphthoic acid.
In the event that an amine (III) is diazotised which is substituted in para-position by the group of the formula Axe2x80x2, a diazo pigment of the formula 
derived from 4,4xe2x80x2-diamino-substituted biphenyl is obtained, wherein the various substituents are as defined above. In the event that an amine (IV) is diazotised, which is substituted in para-position by the group of the formula Bxe2x80x2, a diazo auxochrome derived from 4,4xe2x80x2-diamino substituted biphenyl is obtained. The present invention also relates to pigment mixtures containing diazo-pigments and diazo-auxochromes, which are both derived from diazotised 4,4xe2x80x2-diamino-substituted biphenyls.
If required, the resulting slurry or wet cake of the azo pigment lake may be further processed by treating with an anionic surfactant, such as a fatty acid, a dialkyl sulfosuccinate or resin ester or rosin, or a metal salt, e.g. calcium salt thereof, or with a cationic surfactant, e.g. aliphatic, primary, secondary or tertiary amines, aliphatic diamines or an alkyl quaternary ammonium chloride, or with various known non-ionic surfactants. Usually the amout of surfactants is chosen in the range of from 0 to 50%, preferably from 2 to 35%, most preferably from 5 to 25% by weight, based on the amount of compound I.
The azo lake pigment slurry obtained may then be filtered and washed with water. To improve the dispersibility of the pigments and retain their transparency, the particles may be xe2x80x9cagedxe2x80x9d by stirring the slurry at elevated temperatures, particularly at 70 to 95xc2x0 C. for about 30 minutes up to 3 hours. In a preferred embodiment of the process the composition is further processed to a granular or powder form.
The wet cake of the pigments obtained may be flushed and kneaded directly into a varnish for inks or a resin for paints to prepare a so-called base colour. In a preferred embodiment of the process the wet cake of the composition is further processed to a granular or powder form.
The invention also relates to the process of toning an azo lake pigment composition, which comprises doping the above-mentioned azo lake pigment (I) with an auxochrome (II). The toning may be effected by mixing the azo lake pigment (I) with the auxochrome (II).
The present invention also relates to the use of an auxochrome (II) for toning any azo lake pigments. The invention particularly relates to the use of an auxochrome (II) for toning azo lake pigments (I) as defined above.
The pigment composition according to the present invention can be produced in a fixed quality with excellent reproducibility, and has excellent transparency, a high color strength and a clear and vivid hue.
The combination of the anisidine-based auxochromes (II) mentioned above with Tobias acid coupled onto 2-hydroxy-3-naphthoic acid gives unexpected synergistic improvements in shade, depth and colour strength. The extent of these advantages are unpredictable from additive effects of the auxochrome (II) and the coupling product of 2-napthylamine-1-sulphonic acid (Tobias acid) with the coupling component (V), particularly 2-hydroxy-3-naphthoic acid, in compositions containing pigments of the formula (I).